Lesson 4: Zoonotic viruses

Byadmin

November 10, 2022

Zoonotic viruses are those that can be transmitted from animals to humans, often through direct contact, ingestion of contaminated food or water, or via vectors such as mosquitoes. These viruses are of both veterinary and medical importance due to their impact on animal health, human health, and public health systems.

1. Influenza Virus (Avian and Swine)

  • Family: Orthomyxoviridae
  • Genus: Influenzavirus
  • Hosts: Birds (especially waterfowl), pigs, humans.
  • Transmission: Respiratory droplets, direct contact with infected animals or contaminated environments.
  • Pathogenesis: The virus infects respiratory epithelial cells, leading to respiratory illness and potential systemic complications.
  • Clinical Signs: Fever, cough, sore throat, body aches, in severe cases leading to pneumonia or death.
  • Prevention: Vaccination of animals, biosecurity measures in farms, avoiding contact with infected animals.
  • Veterinary Importance: Causes significant economic losses in poultry industries through outbreaks of highly pathogenic strains (e.g., H5N1).
  • Medical Importance: Some strains (e.g., H5N1, H7N9) can infect humans, leading to severe respiratory disease and high mortality rates.

2. Rabies Virus

  • Family: Rhabdoviridae
  • Genus: Lyssavirus
  • Hosts: Primarily bats, dogs, cats, raccoons, and other mammals.
  • Transmission: Bite or scratch from an infected animal(usually dogs, bats, or wildlife); saliva contact with open wounds or mucous membranes.
  • Pathogenesis: The virus travels along peripheral nerves to the central nervous system, leading to encephalitis.
  • Clinical Signs: Initial symptoms include fever, headache, and malaise, progressing to anxiety, confusion, agitation, hallucinations, hydrophobia, paralysis, and coma.
  • Prevention: Vaccination of pets, avoidance of contact with wild animals, and immediate medical attention following potential exposure.
  • Veterinary Importance: Common in wild and domestic animals. Fatal once clinical signs appear, with a focus on preventing transmission via vaccination of pets.
  • Medical Importance: Fatal in humans if untreated post-exposure. Rabies is preventable through prompt post-exposure prophylaxis (PEP).

3. Hantavirus

  • Family: Hantaviridae
  • Genus: Hantavirus
  • Hosts: Rodents (primarily deer mice).
  • Transmission: Inhalation of aerosolized virus from rodent urine, droppings, or saliva; bites and direct contact are less common.
  • Pathogenesis: The virus affects the endothelium of blood vessels, leading to increased vascular permeability and potential pulmonary or renal syndrome.
  • Clinical Signs: Fever, myalgia, gastrointestinal symptoms, cough, and respiratory distress in severe cases (Hantavirus Pulmonary Syndrome).
  • Prevention: Rodent control, use of protective gear when cleaning rodent-infested areas, proper ventilation.
  • Veterinary Importance: Carried by rodents, though it usually does not cause disease in animals.
  • Medical Importance: Causes Hantavirus Pulmonary Syndrome (HPS) in the Americas and Hemorrhagic Fever with Renal Syndrome (HFRS) in Europe and Asia, both potentially fatal.

4. West Nile Virus (WNV)

  • Family: Flaviviridae
  • Genus: Flavivirus
  • Hosts: Birds (primary), horses, humans.
  • Transmission: Primarily by mosquitoes; also through blood transfusions and organ transplants.
  • Pathogenesis: The virus infects and replicates in the host’s bloodstream and nervous system, leading to neuroinvasion.
  • Clinical Signs: Many cases are asymptomatic; severe cases can cause fever, headache, stiff neck, muscle weakness, seizures, and encephalitis.
  • Prevention: Mosquito control measures, personal protective measures (repellents, long clothing), vaccination of horses.
  • Veterinary Importance: Causes neurological disease in horses and other animals.
  • Medical Importance: In humans, infection can lead to West Nile fever or severe neurological diseases such as meningitis or encephalitis.

5. Nipah Virus

  • Family: Paramyxoviridae
  • Genus: Henipavirus
  • Hosts: Fruit bats (Pteropus species), pigs, humans.
  • Transmission: Direct contact with infected animals, consumption of contaminated food (like raw date palm sap), and person-to-person transmission.
  • Pathogenesis: The virus infects respiratory and nervous systems, leading to encephalitis and respiratory illness.
  • Clinical Signs: Fever, headache, dizziness, respiratory symptoms, confusion, seizures, and in severe cases, coma.
  • Prevention: Avoiding contact with bats and sick animals, hygiene practices, and quarantine measures for outbreaks.
  • Veterinary Importance: Causes respiratory illness and encephalitis in pigs, resulting in high mortality.
  • Medical Importance: In humans, it causes severe respiratory disease and encephalitis, with high fatality rates.

6. Middle East Respiratory Syndrome Coronavirus (MERS-CoV)

  • Family: Coronaviridae
  • Transmission: Close contact with camels or infected humans.
  • Veterinary Importance: Camels are the reservoir host, but they may remain asymptomatic.
  • Medical Importance: Causes severe respiratory illness in humans, with a high mortality rate.

7. Crimean-Congo Hemorrhagic Fever Virus (CCHFV)

  • Family: Nairoviridae
  • Transmission: Tick bites or contact with infected livestock (sheep, goats, cattle).
  • Veterinary Importance: Livestock often show no signs of disease, but they play a role in viral transmission to humans.
  • Medical Importance: Causes a severe hemorrhagic fever with high mortality in humans.

8. Ebola Virus

  • Family: Filoviridae
  • Genus: Ebolavirus
  • Hosts: Fruit bats (likely), nonhuman primates, humans.
  • Transmission: Direct contact with blood, bodily fluids of infected individuals (humans) or animals (e.g., bats, primates) ; handling infected bushmeat.
  • Pathogenesis: The virus damages the endothelial cells, leading to hemorrhagic fever and multi-organ failure.
  • Clinical Signs: Fever, severe headache, joint and muscle pain, diarrhea, vomiting, abdominal pain, and unexplained bleeding.
  • Prevention: Avoiding contact with infected individuals, safe burial practices, vaccination of high-risk populations.
  • Veterinary Importance: Significant outbreaks in non-human primates and some wildlife species.
  • Medical Importance: Causes severe hemorrhagic fever in humans, with a high fatality rate.

9. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

  • Family: Coronaviridae
  • Transmission: Zoonotic origin (likely from bats), with person-to-person transmission via respiratory droplets.
  • Veterinary Importance: Domestic and wild animals have shown susceptibility (e.g., cats, minks), though their role in spreading the virus to humans is limited.
  • Medical Importance: Causes COVID-19 in humans, a global pandemic with significant morbidity and mortality.

10. Zika Virus

  • Family: Flaviviridae
  • Genus: Flavivirus
  • Hosts: Primarily humans and nonhuman primates.
  • Transmission: Mosquito bites (Aedes species), sexual transmission, vertical transmission (maternal-fetal transmission).
  • Pathogenesis: The virus replicates in various tissues, including the central nervous system, potentially leading to complications like microcephaly in newborns.
  • Clinical Signs: Often asymptomatic; symptoms may include fever, rash, conjunctivitis, muscle pain, and headache.
  • Prevention: Mosquito control, use of insect repellent, safe sex practices.
  • Veterinary Importance: Primarily affects non-human primates in nature, with limited veterinary concerns.
  • Medical Importance: Causes Zika fever in humans, typically mild, but associated with serious birth defects (microcephaly) when transmitted in utero.

Importance in One Health Approach

These zoonotic viruses illustrate the close link between animal, human, and environmental health. A collaborative “One Health” approach is essential for preventing and controlling zoonotic diseases by integrating efforts across veterinary and medical fields.

Byadmin